The present invention relates to a fuel cell power generation system.
Since fuel cells have a high power generation efficiency, they will be soon adopted in future power plants, and concrete expedients for making use of the features of them have been proposed. Some of the proposals enhance the overall efficiencies of fuel cell power generation systems. In, for example, Japanese Laid-open Patent Application No. 51-104539, a turbo-charger is driven by waste energy generated within a power plant, and a pressurized gas is used, whereby the efficiencies of a fuel reformer and fuel cells are enhanced. In Japanese Laid-open Patent Application No. 51-104540, steam produced by a cathode is directly used as steam for reformation. In addition, in Japanese Laid-open Patent Application No. 51-104541, steam is generated by the exchange of heat with cells or a shift converter, while waste heat is utilized as heat necessary for the vaporization of water. There are also a proposal as in Japanese Laid-open Patent Application No. 53-29534 wherein steam is generated by the waste heats of a fuel processing device, fuel cell cathodes and a turbo-charger so as to drive a turbo-generator, and one as in Japanese Laid-open Patent Application No. 54-82636 wherein the structure of a hydrogen producing device is improved to enhance the thermal efficiency.
Although these power plants have numerous advantages, they are unsatisfactory as the whole. For example, in order to hold the performance of the fuel cells, it is important to control the temperature of the cells to be constant during stand-by or irrespective of the magnitude of a load. Nevertheless, this is not taken into account or necessitates a systematically delicate control in the foregoing power plants.